Teaching science concepts for conceptual understanding has its challenges. Promoting conceptual change in the science classroom can be difficult because most concepts are complicated and counter-intuitive. This dissertation research aimed to determine the effect of teaching for conceptual understanding models on pre-service teachers' conceptual understanding and grade 8 science students in five different countries. The analysis revealed a statistically significant correlation between the conceptual change model and the conceptual understanding of the pre-service teacher participants. The results supported the effectiveness of the conceptual change model, CCM, in addressing misconceptions and promoting conceptual understanding of forces and motion among the pre-service teacher participants that volunteered for this research. The second study investigated the effectiveness of the CCM in addressing pre-service elementary teachers' misconceptions and promoting conceptual understanding of electrostatics. The results showed that the CCM moderately correlated with participants' conceptual understanding of electrostatics. The third study examined the usage of teaching for conceptual understanding practices and its effects on students' science achievement scores across five industrialized countries. TIMSS 2015 and 2019 data were used to investigate eighth-grade science teachers' use of teaching for conceptual understanding practices. However, the statistical analysis showed that teaching for conceptual understanding had a negative effect on students' science achievement in most of the countries used in the study. This research contributes to the literature on the effect of the conceptual change model and teaching for conceptual understanding on learning science concepts. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]